Question 1

Which of the following statements best explains why oxygen is the most abundant element in the human body by mass?

Accepted Answer

Oxygen is present in water, which makes up a large percentage of the human body.

Question 2

An atom of sodium (Na) has an atomic number of 11 and an atomic mass of 23. How many neutrons does a neutral sodium atom have?

Accepted Answer

$$23 - 11 = 12$$ neutrons

Question 3

Which sub-atomic particle is responsible for the chemical behavior of an atom?

Accepted Answer

Electron

Question 4

Carbon-14 is used in radiometric dating because it decays to nitrogen-14 over time. What property of carbon-14 makes it useful for this purpose?

Accepted Answer

It is a radioactive isotope that decays at a predictable rate.

Question 5

Which of the following best describes the difference between an element and a compound?

Accepted Answer

An element consists of only one type of atom, while a compound consists of two or more elements in a fixed ratio.

Question 6

Which of the following elements is a trace element in the human body, required in very small quantities for life?

Accepted Answer

Iron

Question 7

If an atom has 8 protons, 8 neutrons, and 8 electrons, what is its atomic number and atomic mass?

Accepted Answer

Atomic number: $$8$$, Atomic mass: $$16$$

Question 8

Which of the following best describes an isotope?

Accepted Answer

Atoms of the same element with different numbers of neutrons.

Question 9

Which type of chemical bond involves the sharing of electron pairs between atoms?

Accepted Answer

Covalent bond

Question 10

A neutral atom of chlorine has 17 protons and 18 neutrons. What is its atomic mass?

Accepted Answer

$$17 + 18 = 35$$ amu

Question 11

Which of the following statements about electron shells is correct?

Accepted Answer

Electrons fill the lowest energy shell first.

Question 12

Which of the following is true about noble gases?

Accepted Answer

They have full valence shells and are chemically inert.

Question 13

Which sub-atomic particle has a mass of approximately 1 amu and no electrical charge?

Accepted Answer

Neutron

Question 14

Which of the following best explains why isotopes of the same element have different atomic masses?

Accepted Answer

They have different numbers of neutrons.

Question 15

Which of the following is a correct example of a reversible chemical reaction?

Accepted Answer

$$CO_2 + H_2O$$ \rightleftharpoons H_2CO_3$$

Question 16

Which of the following best describes a molecule?

Accepted Answer

Two or more atoms held together by covalent bonds.

Question 17

Which of the following is NOT a type of chemical bond?

Accepted Answer

Neutron bond

Question 18

Which property of electrons allows them to determine how atoms interact in chemical reactions?

Accepted Answer

Their distribution in electron shells, especially the valence shell

Question 19

A radioactive isotope emits particles and energy as it decays. Which of the following is a biological application of this property?

Accepted Answer

Tracing atoms through metabolic processes

Question 20

Which of the following best explains why compounds have characteristics different from those of their constituent elements?

Accepted Answer

Chemical bonding changes the arrangement of atoms, resulting in new properties.

Chemical Foundation of Life: Atoms and Elements

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